This research proposal is intended to elucidate the efficacy and mechanisms underlying MBCT in a population in remission from recurrent MDD. The first objective of the study is to replicate previous studies'findings of MBCT's effects on decreasing depressive symptoms and depression relapse rates. However, this proposal aims to make a novel contribution to the literature by using a randomized, controlled design, and comparing the effects of MBCT to an active control condition (ACC). The use of a well-designed ACC will enable us to control for confounding variables such as social support and expected outcomes, thus allowing us to determine whether elements specific to MBCT lead to its salutary effects (Aim 1). Previous MBCT studies have largely relied on self-report measurement methodologies, limiting valid conclusions about the nature of MBCT. Further, few studies have examined the mechanisms underlying effects of MBCT on depressive symptoms and relapse. Theoretical considerations and preliminary empirical evidence suggest emotional, physiological, and cognitive functioning to be promising mechanisms of MBCT. Therefore, we propose to assess each of these potential mechanisms of MBCT using self-report, autonomic physiological, and reaction time tasks. (Aim 2). Collectively, these aims are expected to strengthen the evidence base for MBCT while cultivating a scientific model for its effects and mechanisms on decreasing depressive symptoms and depression relapse rates. PUBLIC HEALTH RELEVANCE: The grave public health concern that by 2020 depression will be the second largest contributor to ill-health world-wide has resulted In a surge of interventions aimed at reducing the severity of depressive symptoms and decreasing depression relapse. Some research on CAM treatments for depression suggests meditation to be a promising intervention. In particular, Mindfulness-Based Cognitive Therapy (MBCT), a structured mindfulness meditation intervention, has been shown to reduce depressive symptoms and depression relapse rates associated with recurrent major depressive disorder (MDD). While MBCT studies are promising, further rigorous research must be conducted in order to determine the efficacy, specificity, and mechanisms underlying MBCT for depression. Cultivating empirical support and a scientific model of MBCT is vital to its flourishing therapeutic value, validity, and availability to a diverse population of depression sufferers.